Optical imaging system

ABSTRACT

An optical imaging system includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens, sequentially disposed from an object side to an imaging plane. The optical imaging system satisfies the expression BFL/f&lt;0.15, where BFL represents a distance from an image-side surface of the eighth lens to an imaging plane of an image sensor and f represents an overall focal length of the optical imaging system.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.15/593,391 filed on May 12, 2017, which claims benefit of priority under35 U.S.C. § 119(a) to Korean Patent Application No. 10-2016-0181232filed on Dec. 28, 2016, in the Korean Intellectual Property Office, theentire disclosures of which are incorporated herein by reference for allpurposes.

BACKGROUND 1. Field

The present disclosure relates to an optical imaging system.

2. Description of Related Art

Recently, mobile communications terminals have been provided with cameramodules, enabling image capturing and video calling. In addition, aslevels of functionality of camera modules in mobile communicationsterminals have gradually increased, those camera modules have graduallybeen implemented with higher levels of resolution and performance.

However, because there is a trend for mobile communications terminals tobe miniaturized and lightened, there are limitations in realizing cameramodules having high levels of resolution and performance. In order toprovide miniaturized, light modules, recently camera module lenses havebeen formed of plastic, a material lighter than glass. Optical imagingsystems also have been configured with five or more lenses in order toimplement a high level of resolution.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

According to an aspect of the present disclosure, an optical imagingsystem includes a first lens, a second lens, a third lens, a fourthlens, a fifth lens, a sixth lens, a seventh lens, and an eighth lenssequentially disposed from an object side to an imaging plane, whereinBFL/f<0.15, where BFL represents a distance from an image-side surfaceof the eighth lens to an imaging plane of an image sensor and frepresents an overall focal length of the optical imaging system.

The optical imaging system may satisfy the expression 0.7<TTL/f<1.0,where TTL represents a distance from an object-side surface of the firstlens to the imaging plane of the image sensor. The optical imagingsystem can satisfy the expression f/ImgH<2.9, where ImgH represents ahalf of a diagonal length of the imaging plane of the image sensor. Theoptical imaging system may satisfy the expression −30<f6/f<30, where f6represents a focal length of the sixth lens. The optical imaging systemcan satisfy the expression TTL/ImgH>1.0.

The optical imaging system may further include a stop disposed betweenthe third lens and the fourth lens or between the fourth lens and thefifth lens. The object-side surfaces and image-side surfaces of thefirst to eighth lenses of the optical imaging system can be aspherical.

The optical imaging system may be configured with a first lens having apositive refractive power and a convex object-side surface along anoptical axis. The optical imaging system can be configured with a secondlens having a negative refractive power, a convex object-side surfacealong an optical axis, and a concave image-side surface along theoptical axis. The optical imaging system may be configured with a thirdlens having a positive or negative refractive power, a convexobject-side surface along an optical axis, and a concave image-sidesurface along the optical axis. The optical imaging system can beconfigured with a fourth lens having a positive refractive power, aconvex object-side surface along an optical axis, and a concaveimage-side surface along the optical axis.

The optical imaging system may be configured with a fifth lens having anegative refractive power and a concave image-side surface along anoptical axis. The optical imaging system can be configured with a sixthlens having a positive or negative refractive power and a concaveobject-side surface along an optical axis. The optical imaging systemmay be configured with a seventh lens having a negative refractivepower, a concave object-side surface along an optical axis, and aconcave image-side surface along the optical axis. The optical imagingsystem can be configured with an eighth lens having a positiverefractive power and a convex object-side surface along an optical axis.

In another general aspect, an optical imaging system includes a firstlens, a second lens, a third lens, a fourth lens, a fifth lens, a sixthlens, a seventh lens, and an eighth lens, sequentially disposed from anobject side to an imaging plane. The first to eighth lenses are disposedto be spaced apart from each other by a distance along an optical axis.The expression 0.7<TTL/f<1.0 is satisfied, where TTL represents adistance from an object-side surface of the first lens to an imagingplane of an image sensor and f represents an overall focal length of theoptical imaging system.

In another general aspect, an optical imaging system includes a firstlens having a positive refractive power, a second lens, a third lens, afourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighthlens having a convex object-side surface along an optical axis. Thefirst to eighth lenses are sequentially disposed from an object side toan imaging plane. An F-number of the optical imaging system is 2.4 orless. A field of view (FOV) for the optical imaging system is 40° orless. The expression 0.7<TTL/f<1.0 is satisfied in the optical imagingsystem, where TTL represents a distance from an object-side surface ofthe first lens to an imaging plane of an image sensor and f representsan overall focal length of the optical imaging system.

BRIEF DESCRIPTION OF DRAWINGS

The above and other aspects, features, and advantages of the presentdisclosure will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a view illustrating an optical imaging system according to afirst example;

FIG. 2 is a set of graphs having curves representing aberrationcharacteristics of the optical imaging system illustrated in FIG. 1;

FIG. 3 is a table listing respective characteristics of lenses of theoptical imaging system illustrated in FIG. 1;

FIG. 4 is a table listing respective aspherical coefficients of lensesof the optical imaging system illustrated in FIG. 1;

FIG. 5 is a view illustrating an optical imaging system according to asecond example;

FIG. 6 is a set of graphs having curves representing aberrationcharacteristics of the optical imaging system illustrated in FIG. 5;

FIG. 7 is a table listing respective characteristics of lenses of theoptical imaging system illustrated in FIG. 5;

FIG. 8 is a table listing respective aspherical coefficients of lensesillustrated in FIG. 5;

FIG. 9 is a view illustrating an optical imaging system according to athird example;

FIG. 10 is a set of graphs having curves representing aberrationcharacteristics of the optical imaging system illustrated in FIG. 9;

FIG. 11 is a table listing respective characteristics of lenses of theoptical imaging system illustrated in FIG. 9;

FIG. 12 is a table listing respective aspherical coefficients of lensesof the optical imaging system illustrated in FIG. 9;

FIG. 13 is a view illustrating an optical imaging system according to afourth example;

FIG. 14 is a set of graphs having curves representing aberrationcharacteristics of the optical imaging system illustrated in FIG. 13;

FIG. 15 is a table listing respective characteristics of lenses of theoptical imaging system illustrated in FIG. 13;

FIG. 16 is a table listing respective aspherical coefficients of lensesillustrated in FIG. 13;

FIG. 17 is a view illustrating an optical imaging system according to afifth example;

FIG. 18 is a set of graphs having curves representing aberrationcharacteristics of the optical imaging system illustrated in FIG. 17;

FIG. 19 is a table listing respective characteristics of lenses of theoptical imaging system illustrated in FIG. 17;

FIG. 20 is a table listing respective aspherical coefficients of lensesillustrated in FIG. 17;

FIG. 21 is a view illustrating an optical imaging system according to asixth example;

FIG. 22 is a set of graphs having curves representing aberrationcharacteristics of the optical imaging system illustrated in FIG. 21;

FIG. 23 is a table listing respective characteristics of lenses of theoptical imaging system illustrated in FIG. 21; and

FIG. 24 is a table listing respective aspherical coefficients of lensesof the optical imaging system illustrated in FIG. 21.

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements, where applicable. The drawings maynot be to scale, and the relative size, proportions, and depiction ofelements in the drawings may be exaggerated for clarity, illustration,or convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the methods, apparatuses, and/orsystems described herein will be apparent after an understanding of thedisclosure. The sequences of operations described herein are merelyexamples, and are not limited to those set forth herein, but may bechanged, as will be apparent after an understanding of the disclosure,with the exception of operations necessarily occurring in a certainorder. Also, descriptions of functions and constructions that are wellknown may be omitted for increased clarity and conciseness.

The features described herein may be embodied in different forms, andshould not be construed as being limited to the examples describedherein. Rather, the examples described herein have been provided so thatthis disclosure will be thorough and complete, and will convey the fullscope of the disclosure to one of ordinary skill in the art.

Throughout the specification, it will be understood that when anelement, such as a layer, region or wafer (substrate), is referred to asbeing “on,” “connected to,” or “coupled to” another element, it can bedirectly “on,” “connected to,” or “coupled to” the other element, orother elements intervening therebetween may be present. In contrast,when an element is referred to as being “directly on,” “directlyconnected to,” or “directly coupled to” another element, there may be noelements or layers intervening therebetween. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

The articles “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. The terms“comprises,” “includes,” and “has” specify the presence of statedfeatures, numbers, operations, members, elements, and/or combinationsthereof, but do not preclude the presence or addition of one or moreother features, numbers, operations, members, elements, and/orcombinations thereof.

Due to manufacturing techniques and/or tolerances, variations of theshapes shown in the drawings may occur. Thus, the examples describedherein are not limited to the specific shapes shown in the drawings, butinclude changes in shape that occur during manufacturing.

Hereinafter, embodiments of the present disclosure will now be describedin detail with reference to the accompanying drawings. Examples of thepresent disclosure provide an optical imaging system having a narrowfield of view while retaining a thin width. Examples of the presentdisclosure also provide an optical imaging system in which an aberrationcorrection is improved and a high level of resolution is implemented.

In the drawings, the thicknesses, sizes, and shapes of lenses have beenslightly exaggerated for convenience of explanation. Particularly, theshapes of spherical surfaces or aspherical surfaces illustrated in thedrawings are illustrated by way of example. That is, the shapes of thespherical surfaces or the aspherical surfaces are not limited to thoseillustrated in the drawings.

Although terms such as “first,” “second,” and “third” may be used hereinto describe various components, regions, or sections, these components,regions, or sections are not to be limited by these terms, unlessotherwise specifically noted such as in the below instances. Rather,these terms are only used to distinguish one component, region, orsection from another component, region, or section. Thus, a firstcomponent, region, or section referred to in examples described hereinmay also be referred to as a second component, region, or sectionwithout departing from the teachings of the examples. However, in thepresent specification, a first lens refers to a lens closest to anobject, while an eighth lens refers to a lens closest to an imagesensor. In addition, a first surface of each lens refers to a surface ofthe lens closest to an object side (or an object-side surface) and asecond surface of each lens refers to a surface of the lens closest toan image side (or an image-side surface).

In accordance with illustrative examples, the embodiments described ofthe optical system include eight lenses with a refractive power.However, the number of lenses in the optical system may vary in someembodiments, for example, between two to eight lenses, while achievingone or more results and benefits described below. Also, although eachlens is described with a particular refractive power, a differentrefractive power for at least one of the lenses may be used to achievethe intended result.

Further, all numerical values of radii of curvature and thicknesses oflenses, and the like, are denoted in millimeters (mm), and a field ofview (FOV) of an optical imaging system is indicated by degrees. Aperson skilled in the relevant art will appreciate that other units ofmeasurement may be used. Further, in embodiments, all radii ofcurvature, thicknesses, OALs (optical axis distances from the firstsurface of the first lens to the image sensor), a distance on theoptical axis between the stop and the image sensor (SLs), image heights(IMGHs) (image heights), and back focus lengths (BFLs) of the lenses, anoverall focal length of an optical system, and a focal length of eachlens are indicated in millimeters (mm). Likewise, thicknesses of lenses,gaps between the lenses, OALs, TLs, SLs are distances measured based onan optical axis of the lenses.

Further, in a description for a shape of each of the lenses, the meaningthat one surface of a lens is convex is that a paraxial region portionof a corresponding surface is convex, and the meaning that one surfaceof a lens is concave is that a paraxial region portion of acorresponding surface is concave. Therefore, although it is describedthat one surface of a lens is convex, an edge portion of the lens may beconcave. Likewise, although it is described that one surface of a lensis concave, an edge portion of the lens may be convex. Meanwhile, aparaxial region refers to a very narrow region in the vicinity of anoptical axis. In other words, a paraxial region of a lens may be convex,while the remaining portion of the lens outside the paraxial region iseither convex, concave, or flat. Further, a paraxial region of a lensmay be concave, while the remaining portion of the lens outside theparaxial region is either convex, concave, or flat. In addition, in anembodiment, thicknesses and radii of curvatures of lenses are measuredin relation to optical axes of the corresponding lenses.

An optical imaging system according to embodiments in the presentdisclosure may include eight lenses. For example, the optical imagingsystem according to the embodiments may include a first lens, a secondlens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventhlens, and an eighth lens sequentially disposed from the object side toan imaging plane. However, the optical imaging system according to theembodiments is not limited to only including lenses, but may furtherinclude additional components. For example, the optical imaging systemmay further include an image sensor converting an image of a subjectincident on the image sensor into an electrical signal.

In addition, the optical imaging system may further include an infraredcut-off filter filtering infrared light. The infrared cut-off filter maybe disposed between the eighth lens and the image sensor. In addition,the optical imaging system may further include a stop controlling anamount of light. As examples, the stop may be disposed between the thirdlens and the fourth lens or between the fourth lens and the fifth lens.

In the optical imaging system according to the embodiments, the first toeighth lenses may be formed of plastic. In addition, at least one of thefirst to eighth lenses may have an aspherical surface. Further, each ofthe first to eighth lenses may have at least one aspherical surface.That is, at least one of first and second surfaces of all of the firstto eighth lenses may be aspherical. The aspherical surfaces of the firstto eighth lenses may be represented by the following Equation 1:

$\begin{matrix}{Z = {\frac{{cY}^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right)c^{2}Y^{2}}}} + {AY}^{4} + {BY}^{6} + {CY}^{8} + {DY}^{10} + {EY}^{12} + {FY}^{14} + {\ldots \mspace{14mu}.}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, c represents a curvature (an inverse of a radius of curvature) ofa lens, K represents a conic constant, and Y represents a distance froma certain point on an aspherical surface of the lens to an optical axisin a direction perpendicular to the optical axis. In addition, constantsA to F represent aspherical coefficients. Further in Equation 1, Zrepresents a distance between the certain point on the asphericalsurface of the lens at the distance Y and a tangential plane meeting theapex of the aspherical surface of the lens.

The optical imaging system including the first to eighth lenses mayrespectively have a positive refractive power, a negative refractivepower, a positive refractive power, a positive refractive power, anegative refractive power, a positive refractive power, a negativerefractive power, and a positive refractive power, sequentially from theobject side to the imaging plane.

The optical imaging system according to embodiments may satisfy thefollowing Conditional Expressions:

BFL/f<0.15  [Conditional Expression 1]

0.7<TTL/f<1.0  [Conditional Expression 2]

f/ImgH<2.9  [Conditional Expression 3]

−30<f6/f<30  [Conditional Expression 4]

TTL/ImgH>1.0.  [Conditional Expression 5]

Here, f represents an overall focal length of the optical imagingsystem, BFL represents a distance from an image-side surface of theeighth lens to an imaging plane of the image sensor, TTL represents adistance from an object-side surface of the first lens to the imagingplane of the image sensor, ImgH represents a half of a diagonal lengthof the imaging plane of the image sensor, and f6 represents a focallength of the sixth lens.

TABLE 1 First Exemplary Second Exemplary Third Exemplary FourthExemplary Fifth Exemplary Sixth Exemplary Embodiment EmbodimentEmbodiment Embodiment Embodiment Embodiment TTL/f 0.893 0.853 0.8420.832 0.944 0.833 BFL/f 0.130 0.095 0.095 0.095 0.149 0.100 f/ImgH 2.8352.835 2.835 2.835 2.686 2.686 f6/f 11.256 −5.640 −4.747 −1.569 9.601−27.026 TTL/ImgH 1.265 1.209 1.194 1.179 1.268 1.119

Next, the first to eighth lenses constituting the optical imaging systemaccording to the examples will be described. The first lens may have apositive refractive power. In addition, the first lens may have ameniscus shape of which an object-side surface is convex. In anembodiment, a first surface of the first lens is convex in the paraxialregion and a second surface is concave in the paraxial region.Alternatively, in other embodiments both surfaces of the first lens maybe convex. At least one of the first and second surfaces of the firstlens may be aspherical. For example, both surfaces of the first lens areaspherical.

The second lens may have a negative refractive power. In addition, thesecond lens may have a meniscus shape of which an object-side surface isconvex. In an embodiment, a first surface of the second lens is convexin the paraxial region and a second surface is concave in the paraxialregion. At least one of the first and second surfaces of the second lensmay be aspherical. For example, both surfaces of the second lens areaspherical.

The third lens may have a positive or negative refractive power. Inaddition, the third lens may have a meniscus shape of which anobject-side surface is convex. In an embodiment, a first surface of thethird lens is convex in the paraxial region and a second surface isconcave in the paraxial region. At least one of the first and secondsurfaces of the third lens may be aspherical. For example, both surfacesof the third lens are aspherical.

The fourth lens may have a positive refractive power. In addition, thefourth lens may have a meniscus shape of which an object-side surface isconvex. In an embodiment, a first surface of the fourth lens is convexin the paraxial region and a second surface is concave in the paraxialregion. At least one of the first and second surfaces of the fourth lensmay be aspherical. For example, both surfaces of the fourth lens areaspherical.

The fifth lens may have a negative refractive power. In addition, bothsurfaces of the fifth lens may be concave. In an embodiment, first andsecond surfaces of the fifth lens are concave. Alternatively, the fifthlens may have a meniscus shape of which an object-side surface isconvex. In an alternative embodiment, a first surface of the fifth lensmay be convex in the paraxial region and a second surface is concave inthe paraxial region. At least one of the first and second surfaces ofthe fifth lens may be aspherical. For example, both surfaces of thefifth lens are aspherical.

The sixth lens may have a positive or negative refractive power. Inaddition, the sixth lens may have a meniscus shape of which animage-side surface is convex. In an embodiment, a first surface of thesixth lens is concave in the paraxial region and a second surface isconvex in the paraxial region. Alternatively, both surfaces of the sixthlens may be concave. In an alternative embodiment, the first and secondsurfaces of the sixth lens may be concave. At least one of the first andsecond surfaces of the sixth lens may be aspherical. For example, bothsurfaces of the sixth lens are aspherical.

The seventh lens may have a negative refractive power. In addition, bothsurfaces of the seventh lens may be concave. In an embodiment, first andsecond surfaces of the seventh lens are concave in the paraxial region.At least one of the first and second surfaces of the seventh lens may beaspherical. For example, both surfaces of the seventh lens areaspherical.

In addition, at least one inflection point may be formed on one or bothof the first and second surfaces of the seventh lens. For example, thefirst surface of the seventh lens is concave in the paraxial region andbecomes convex toward an edge of the lens. In addition, the secondsurface of the seventh lens is concave in the paraxial region andbecomes convex at an edge of the lens.

The eighth lens may have a positive refractive power. In addition, bothsurfaces of the eighth lens may be convex. In an embodiment, the firstand second surfaces of the eighth lens are convex. Alternatively, theeighth lens may have a meniscus shape of which an object-side surface isconvex. In an alternative embodiment, a first surface of the eighth lensmay be convex in the paraxial region, and a second surface may beconcave in the paraxial region.

At least one of the first and second surfaces of the eighth lens may beaspherical. For example, both surfaces of the eighth lens areaspherical. In addition, at least one inflection point may be formed onthe second surface of the eighth lens. For example, the second surfaceof the eighth lens is concave in the paraxial region and becomes convextoward an edge of the lens.

In the optical imaging system configured as described above, a pluralityof lenses may perform an aberration correction function to increaseaberration correction. In addition, in the optical imaging systemsaccording to the embodiments, a constant (F-number) indicatingbrightness of the optical imaging system is 2.4 or less. Therefore, theoptical imaging systems may clearly capture an image even in anenvironment in which illumination is low. In addition, the opticalimaging systems according to the embodiments may have a telephoto ratio(TTL/f) smaller than 1 to have features of a telephoto lens and have afield of view (FOV) of 40° or less. Therefore, a narrow FOV isimplemented.

An optical imaging system according to a first example in the presentdisclosure will be described with reference to FIGS. 1 through 4. Theoptical imaging system according to the first example includes a firstlens 110, a second lens 120, a third lens 130, a fourth lens 140, afifth lens 150, a sixth lens 160, a seventh lens 170, and an eighth lens180. The optical imaging system according to the first example mayfurther include a stop ST, an infrared cut-off filter 190, and an imagesensor 191.

Respective characteristics (radii of curvature, thicknesses or distancesbetween lenses, refractive indices, and Abbe numbers) of lenses arelisted in FIG. 3. Meanwhile, by way of example, a focal length (f1) ofthe first lens is 4.622 mm, a focal length (f2) of the second lens is−7.990 mm, a focal length (f3) of the third lens is 22.288 mm, a focallength (f4) of the fourth lens is 38.607 mm, a focal length (f5) of thefifth lens is −11.193 mm, a focal length (f6) of the sixth lens is106.931 mm, a focal length (f7) of the seventh lens is −7.066 mm, and afocal length (f8) of the eighth lens is 18.325 mm. In addition, for theoptical imaging system according to the first example, BFL/f is 0.13,TTL/f is 0.893, f/ImgH is 2.835, f6/f is 11.256, and TTL/ImgH is 1.265.

In the first example, the first lens 110 has a positive refractivepower, a convex first surface in the paraxial region and a concavesecond surface in the paraxial region. The second lens 120 has anegative refractive power, a convex first surface in the paraxialregion, and a concave second surface in the paraxial region. The thirdlens 130 has a positive refractive power, a convex first surface in theparaxial region, and a concave second surface in the paraxial region.The fourth lens 140 has a positive refractive power, a convex firstsurface in the paraxial region, and a concave second surface in theparaxial region.

The fifth lens 150 has a negative refractive power and concave first andsecond surfaces in the paraxial region. The sixth lens 160 has apositive refractive power, a concave first surface in the paraxialregion, and a convex second surface in the paraxial region. The seventhlens 170 has a negative refractive power and concave first and secondsurfaces in the paraxial region. In addition, at least one inflectionpoint may be formed on one or both of the first and second surfaces ofseventh lens 170. For example, the first surface of seventh lens 170 isconcave in a paraxial region and becomes convex toward an edge of lens170. In addition, the second surface of seventh lens 170 is concave inthe paraxial region and becomes convex at an edge of lens 170. Theeighth lens 180 has a positive refractive power, and a convex firstsurface and a convex second surface in the paraxial region.

Respective surfaces of first to eighth lenses 110 to 180 have asphericalcoefficients as listed in FIG. 4. For example, all of object-sidesurfaces and image-side surfaces of first to eighth lenses 110 to 180are aspherical. Optionally, stop ST is disposed between third lens 130and fourth lens 140. The optical imaging system configured as describedabove has aberration characteristics as illustrated by the graphs inFIG. 2.

An optical imaging system according to a second example in the presentdisclosure will be described with reference to FIGS. 5 through 8. Theoptical imaging system according to the second example includes a firstlens 210, a second lens 220, a third lens 230, a fourth lens 240, afifth lens 250, a sixth lens 260, a seventh lens 270, and an eighth lens280. The optical imaging system according to the second example mayfurther include a stop ST, an infrared cut-off filter 290, and an imagesensor 291.

Respective characteristics (radii of curvature, thicknesses or distancesbetween lenses, refractive indices, and Abbe numbers) of lenses arelisted in FIG. 7. Meanwhile, by way of example, a focal length (f1) ofthe first lens is 4.6171 mm, a focal length (f2) of the second lens is−7.8634 mm, a focal length (f3) of the third lens is 21.3041 mm, a focallength (f4) of the fourth lens is 31.1721 mm, a focal length (f5) of thefifth lens is −10.1467 mm, a focal length (f6) of the sixth lens is−53.5815 mm, a focal length (f7) of the seventh lens s −7.0016 mm, and afocal length (f8) of the eighth lens is 18.1526 mm. In addition, for theoptical imaging system according to the second example, BFL/f is 0.095,TTL/f is 0.853, f/ImgH is 2.835, f6/f is −5.64, and TTL/ImgH is 1.209.

In the second example, first lens 210 has a positive refractive power, aconvex first surface in the paraxial region, and a concave secondsurface in the paraxial region. The second lens 220 has a negativerefractive power, a convex first surface in the paraxial region, and aconcave second surface in the paraxial region. The third lens 230 has apositive refractive power, a convex first surface in the paraxialregion, and a concave second surface in the paraxial region. The fourthlens 240 has a positive refractive power, a convex first surface in theparaxial region, and a concave second surface in the paraxial region.

The fifth lens 250 has a negative refractive power and concave firstsurface and second surfaces in the paraxial region. The sixth lens 260has a negative refractive power, a concave first surface in the paraxialregion, and a convex second surface in the paraxial region. The seventhlens 270 has a negative refractive power and concave first and secondsurfaces in the paraxial region. In addition, at least one inflectionpoint may be formed on one or both of the first and second surfaces ofseventh lens 270. For example, the first surface of seventh lens 270 isconcave in a paraxial region and becomes convex toward an edge of lens270. In addition, the second surface of seventh lens 270 is concave inthe paraxial region and becomes convex at an edge of lens 270. Theeighth lens 280 has a positive refractive power and convex first andsecond surfaces in the paraxial region.

Meanwhile, respective surfaces of first to eighth lenses 210 to 280 haveaspherical coefficients as listed in FIG. 8. For example, all ofobject-side surfaces and image-side surfaces of first to eighth lenses210 to 280 are aspherical. Optionally, stop ST is disposed between thirdlens 230 and fourth lens 240. The optical imaging system configured asdescribed above has aberration characteristics as illustrated by thegraphs in FIG. 6.

An optical imaging system according to a third example in the presentdisclosure will be described with reference to FIGS. 9 through 12. Theoptical imaging system according to the third example includes a firstlens 310, a second lens 320, a third lens 330, a fourth lens 340, afifth lens 350, a sixth lens 360, a seventh lens 370, and an eighth lens380. The optical imaging system according to the third example mayfurther include a stop ST, an infrared cut-off filter 390, and an imagesensor 391.

Respective characteristics (radii of curvature, thicknesses or distancesbetween lenses, refractive indices, and Abbe numbers) of lenses arelisted in FIG. 11. Meanwhile, by way of example, a focal length (f1) ofthe first lens is 4.5688 mm, a focal length (f2) of the second lens is−7.667 mm, a focal length (f3) of the third lens is 15.6031 mm, a focallength (f4) of the fourth lens is 35.7796 mm, a focal length (f5) of thefifth lens is −7.4186 mm, a focal length (f6) of the sixth lens is−45.0951 mm, a focal length (f7) of the seventh lens is −8.6419 mm, anda focal length (f8) of the eighth lens is 25.7824 mm. In addition, forthe optical imaging system according to the third example, BFL/f is0.095, TTL/f is 0.842, f/ImgH is 2.835, f6/f is −4.747, and TTL/ImgH is1.194.

In the third example, the first lens 310 has a positive refractivepower, a convex first surface in the paraxial region, and a concavesecond surface in the paraxial region. The second lens 320 has anegative refractive power, a convex first surface in the paraxialregion, and a concave second surface in the paraxial region. The thirdlens 330 has a positive refractive power, a convex first surface in theparaxial region, and a concave second surface in the paraxial region.The fourth lens 340 has a positive refractive power, a convex firstsurface in the paraxial region, and a concave second surface in theparaxial region.

The fifth lens 350 has a negative refractive power and concave first andsecond surfaces in the paraxial region. The sixth lens 360 has anegative refractive power, a concave first surface in the paraxialregion, and a convex second surface in the paraxial region. The seventhlens 370 has a negative refractive power and concave first and secondsurfaces in the paraxial region. In addition, at least one inflectionpoint may be formed on one or both of the first and second surfaces ofthe seventh lens 370. For example, the first surface of seventh lens 370is concave in a paraxial region and becomes convex toward an edge oflens 370. In addition, the second surface of seventh lens 370 is concavein the paraxial region and becomes convex at an edge of lens 370. Theeighth lens 380 has a positive refractive power and convex first andsecond surfaces in the paraxial region.

Respective surfaces of first to eighth lenses 310 to 380 have asphericalcoefficients as listed in FIG. 12. For example, all of object-sidesurfaces and image-side surfaces of first to eighth lenses 310 to 380are aspherical. Optionally, stop ST is disposed between third lens 330and fourth lens 340. In addition, the optical imaging system configuredas described above has aberration characteristics as illustrated by thegraphs in FIG. 10.

An optical imaging system according to a fourth example in the presentdisclosure will be described with reference to FIGS. 13 through 16. Theoptical imaging system according to the fourth example includes a firstlens 410, a second lens 420, a third lens 430, a fourth lens 440, afifth lens 450, a sixth lens 460, a seventh lens 470, and an eighth lens480. The optical imaging system according to the fourth example mayfurther include a stop ST, an infrared cut-off filter 490, and an imagesensor 491.

Respective characteristics (radii of curvature, thicknesses or distancesbetween lenses, refractive indices, and Abbe numbers) of lenses arelisted in FIG. 15. Meanwhile, by way of example, a focal length (f1) ofthe first lens is 4.5911 mm, a focal length (f2) of the second lens is−7.433 mm, a focal length (f3) of the third lens is 15.5555 mm, a focallength (f4) of the fourth lens is 27.9197 mm, a focal length (f5) of thefifth lens is −8.634 mm, a focal length (f6) of the sixth lens is−14.9025 mm, a focal length (f7) of the seventh lens is −7.3676 mm, anda focal length (f8) of the eighth lens is 12.3205 mm. In addition, forthe optical imaging system according to the fourth example, BFL/f is0.095, TTL/f is 0.832, f/ImgH is 2.835, f6/f is −1.569, and TTL/ImgH is1.179.

In the fourth example, the first lens 410 has a positive refractivepower, a convex first surface in the paraxial region, and a concavesecond surface in the paraxial region. The second lens 420 has anegative refractive power, a convex first surface in the paraxialregion, and a concave second surface in the paraxial region. The thirdlens 430 has a positive refractive power, a convex first surface in theparaxial region, and a concave second surface in the paraxial region.The fourth lens 440 has a positive refractive power, a convex firstsurface in the paraxial region, and a concave second surface in theparaxial region.

The fifth lens 450 has a negative refractive power and concave first andsecond surfaces in the paraxial region. The sixth lens 460 has anegative refractive power and concave first surface and second surfacesin the paraxial region. The seventh lens 470 has a negative refractivepower and concave first and second surfaces in the paraxial region. Inaddition, at least one inflection point may be formed on one or both ofthe first and second surfaces of seventh lens 470. For example, thefirst surface of seventh lens 470 is concave in a paraxial region andbecomes convex toward an edge of lens 470. In addition, the secondsurface of seventh lens 470 is concave in the paraxial region andbecomes convex at an edge of lens 470. The eighth lens 480 has apositive refractive power and convex first and second surfaces in theparaxial region.

Respective surfaces of first to eighth lenses 410 to 480 have asphericalcoefficients as listed in FIG. 16. For example, all of object-sidesurfaces and image-side surfaces of first to eighth lenses 410 to 480are aspherical. Optionally, stop ST is disposed between fourth lens 440and fifth lens 450. In addition, the optical imaging system configuredas described above has aberration characteristics as illustrated by thegraphs in FIG. 14.

An optical imaging system according to a fifth example in the presentdisclosure will be described with reference to FIGS. 17 through 20. Theoptical imaging system according to the fifth example includes a firstlens 510, a second lens 520, a third lens 530, a fourth lens 540, afifth lens 550, a sixth lens 560, a seventh lens 570, and an eighth lens580. The optical imaging system according to the fifth example mayfurther include a stop ST, an infrared cut-off filter 590, and an imagesensor 591.

Respective characteristics (radii of curvature, thicknesses or distancesbetween lenses, refractive indices, and Abbe numbers) of lenses arelisted in FIG. 19. Meanwhile, by way of example, a focal length (f1) ofthe first lens is 4.5945 mm, a focal length (f2) of the second lens is−10.0201 mm, a focal length (f3) of the third lens is −615.7002 mm, afocal length (f4) of the fourth lens is 1017.38 mm, a focal length (f5)of the fifth lens is −24.508 mm, a focal length (f6) of the sixth lensis 86.4093 mm, a focal length (f7) of the seventh lens is −6.5688 mm,and a focal length (f8) of the eighth lens is 15.8206 mm. In addition,for the optical imaging system according to the fifth example, BFL/f is0.149, TTL/f is 0.944, f/ImgH is 2.686, f6/f is 9.601, and TTL/ImgH is1.268.

In the fifth example, the first lens 510 has a positive refractive powerand convex first and second surfaces in the paraxial region. The secondlens 520 has a negative refractive power, a convex first surface in theparaxial region, and a concave second surface in the paraxial region.The third lens 530 has a negative refractive power, a convex firstsurface in the paraxial region, and a concave second surface in theparaxial region. The fourth lens 540 has a positive refractive power, aconvex first surface in the paraxial region, and a concave secondsurface in the paraxial region.

The fifth lens 550 has a negative refractive power, a convex firstsurface in the paraxial region, and a concave second surface in theparaxial region. The sixth lens 560 has a positive refractive power, aconcave first surface in the paraxial region, and a convex secondsurface in the paraxial region. The seventh lens 570 has a negativerefractive power and concave first and second surfaces in the paraxialregion. In addition, at least one inflection point may be formed on oneor both of the first and second surfaces of seventh lens 570. Forexample, the first surface of seventh lens 570 is concave in a paraxialregion and becomes convex toward an edge of lens 570. In addition, thesecond surface of seventh lens 570 is concave in the paraxial region andbecomes convex at an edge of lens 570. The eighth lens 580 has apositive refractive power and convex first and second surfaces in theparaxial region.

Respective surfaces of first to eighth lenses 510 to 580 have asphericalcoefficients as listed in FIG. 20. For example, all of object-sidesurfaces and image-side surfaces of first to eighth lenses 510 to 580are aspherical. Optionally, stop ST is disposed between third lens 530and fourth lens 540. In addition, the optical imaging system configuredas described above has aberration characteristics as illustrated by thegraphs in FIG. 18.

An optical imaging system according to a sixth example in the presentdisclosure will be described with reference to FIGS. 21 through 24. Theoptical imaging system according to the sixth example includes a firstlens 610, a second lens 620, a third lens 630, a fourth lens 640, afifth lens 650, a sixth lens 660, a seventh lens 670, and an eighth lens680. The optical imaging system according to the sixth example mayfurther include a stop ST, an infrared cut-off filter 690, and an imagesensor 691.

Respective characteristics (radii of curvature, thicknesses or distancesbetween lenses, refractive indices, and Abbe numbers) of lenses arelisted in FIG. 23. Meanwhile, by way of example, a focal length (f 1) ofthe first lens is 4.4844 mm, a focal length (f2) of the second lens is−7.3212 mm, a focal length (f3) of the third lens is 12.1061 mm, a focallength (f4) of the fourth lens is 29.3566 mm, a focal length (f5) of thefifth lens is −5.8446 mm, a focal length (f6) of the sixth lens is−243.2353 mm, a focal length (f7) of the seventh lens is −8.4043 mm, anda focal length (f8) of the eighth lens is 120.4209 mm. In addition, forthe optical imaging system according to the sixth example, BFL/f is 0.1,TTL/f is 0.833, f/ImgH is 2.686, f6/f is −27.026, and TTL/ImgH is 1.119.

In the sixth embodiment, the first lens 610 has a positive refractivepower, a convex first surface in the paraxial region, and a concavesecond surface in the paraxial region. The second lens 620 has anegative refractive power, a convex first surface in the paraxialregion, and a concave second surface in the paraxial region. The thirdlens 630 has a positive refractive power, a convex first surface in theparaxial region, and a concave second surface in the paraxial region.The fourth lens 640 has a positive refractive power, a convex firstsurface in the paraxial region, and a concave second surface in theparaxial region.

The fifth lens 650 has a negative refractive power and concave first andsecond surfaces in the paraxial region. The sixth lens 660 has anegative refractive power, a concave first surface in the paraxialregion, and a convex second surface in the paraxial region. The seventhlens 670 has a negative refractive power and concave first and secondsurfaces in the paraxial region. In addition, at least one inflectionpoint may be formed on one or both of the first and second surfaces ofseventh lens 670. For example, the first surface of seventh lens 670 isconcave in a paraxial region and becomes convex toward an edge of lens670. In addition, the second surface of seventh lens 670 is concave inthe paraxial region and becomes convex at an edge of lens 670. Theeighth lens 680 has a positive refractive power, a convex first surfacein the paraxial region, and a concave second surface in the paraxialregion. In addition, at least one inflection point may be formed on thesecond surface of eighth lens 680. For example, the second surface ofeighth lens 680 is concave in the paraxial region and becomes convextoward an edge of lens 680.

Respective surfaces of first to eighth lenses 610 to 680 have asphericalcoefficients as listed in FIG. 24. For example, all of object-sidesurfaces and image-side surfaces of first to eighth lenses 610 to 680are aspherical. Optionally, stop ST is disposed between fourth lens 640and fifth lens 650. In addition, the optical imaging system configuredas described above has aberration characteristics as illustrated by thegraphs in FIG. 22.

As set forth above, according to embodiments in the present disclosure,an optical imaging system having a narrow field of view whilemaintaining a thin width may be implemented. In addition, an improvedaberration correction effect may be realized, and a high level ofresolution may be implemented. While embodiments have been shown anddescribed above, it will be apparent to those after an understanding ofthe disclosure that modifications and variations could be made withoutdeparting from the scope of the present application as defined by theappended claims.

What is claimed is:
 1. An optical imaging system comprising: a firstlens, a second lens, a third lens, a fourth lens, a fifth lens, a sixthlens, a seventh lens, and an eighth lens sequentially disposed from anobject side to an imaging plane, wherein BFL/f<0.15, where BFLrepresents a distance from an image-side surface of the eighth lens toan imaging plane of an image sensor and f represents an overall focallength of an optical system including the first to eighth lenses.
 2. Theoptical imaging system of claim 1, wherein 0.7<TTL/f<1.0, where TTLrepresents a distance from an object-side surface of the first lens tothe imaging plane of the image sensor.
 3. The optical imaging system ofclaim 1, wherein f/ImgH<2.9, where ImgH represents a half of a diagonallength of the imaging plane of the image sensor.
 4. The optical imagingsystem of claim 1, wherein −30<f6/f<30, where f6 represents a focallength of the sixth lens.
 5. The optical imaging system of claim 1,wherein TTL/ImgH>1.0, where TTL represents a distance from anobject-side surface of the first lens to the imaging plane of the imagesensor and ImgH represents a half of a diagonal length of the imagingplane of the image sensor.
 6. The optical imaging system of claim 1,further comprising a stop disposed between the third lens and the fourthlens or between the fourth lens and the fifth lens.
 7. The opticalimaging system of claim 1, wherein object-side surfaces and image-sidesurfaces of the first to eighth lenses are aspherical.
 8. The opticalimaging system of claim 1, wherein the first lens has a positiverefractive power and a convex object-side surface along an optical axis.9. The optical imaging system of claim 1, wherein the second lens has anegative refractive power, a convex object-side surface along an opticalaxis, and a concave image-side surface along the optical axis.
 10. Theoptical imaging system of claim 1, wherein the third lens has a positiveor negative refractive power, a convex object-side surface along anoptical axis, and a concave image-side surface along the optical axis.11. The optical imaging system of claim 1, wherein the fourth lens has apositive refractive power, a convex object-side surface along an opticalaxis, and a concave image-side surface along the optical axis.
 12. Theoptical imaging system of claim 1, wherein the fifth lens has a negativerefractive power and a concave image-side surface along an optical axis.13. The optical imaging system of claim 1, wherein the sixth lens has apositive or negative refractive power and a concave object-side surfacealong an optical axis.
 14. The optical imaging system of claim 1,wherein the seventh lens has a negative refractive power, a concaveobject-side surface along an optical axis, and a concave image-sidesurface along the optical axis.
 15. The optical imaging system of claim1, wherein the eighth lens has a positive refractive power and a convexobject-side surface along an optical axis.
 16. An optical imaging systemcomprising: a first lens, a second lens, a third lens, a fourth lens, afifth lens, a sixth lens, a seventh lens, and an eighth lens,sequentially disposed from an object side to an imaging plane, whereinthe first to eighth lenses are disposed to be spaced apart from eachother by a distance along an optical axis, and wherein 0.7<TTL/f<1.0,where TTL represents a distance from an object-side surface of the firstlens to an imaging plane of an image sensor and f represents an overallfocal length of the optical imaging system.
 17. An optical imagingsystem comprising: a first lens having a positive refractive power; asecond lens, a third lens, a fourth lens, a fifth lens, a sixth lens,and a seventh lens; an eighth lens having a convex object-side surfacealong an optical axis, wherein the first to eighth lenses aresequentially disposed from an object side to an imaging plane, whereinan F-number of the optical imaging system is 2.4 or less, wherein afield of view (FOV) of the optical imaging system is 40° or less, andwherein 0.7<TTL/f<1.0, where TTL represents a distance from anobject-side surface of the first lens to an imaging plane of an imagesensor and f represents an overall focal length of the optical imagingsystem.